An earthquake occurs because of the movements of tectonic plates beneath the surface of the earth. These movements create waves which propagate through the earth. These waves are known as seismic waves. It causes mild to heavy shaking and vibrations. The intensity of these vibrations can vary, but sometimes they can bring about great destruction. Earthquake in oceans is known as Tsunami, which is equally devastating.
Earthquakes can be human-made or natural, although the latter is more abundant. These earthquakes are not random; rather they are the effect of different changes occurring in earth’s crust for a long time. The main causes of earthquakes fall into five categories:
1. Volcanic Eruptions
The main cause of earthquake is volcanic eruptions. Such type of earthquakes occurs in areas, with frequent volcanic activities. When boiling lava tries to break through the surface of the earth, with the increased pressure of gases, certain movements are caused in earth’s crust. Movement of lava beneath the surface of the earth can also cause certain disruptions. This sends shockwaves through the earth, causing damage. These earthquakes are mild. Their range is also limited. However, there have been certain exceptions, with volcanic earthquakes bring havoc and death to thousands of people.
2. Tectonic Movements
The surface of the earth consists of some plates, comprising of the upper mantle. These plates are always moving, thus effecting earth’s crust. These movements are categorized into three types: constructive, destructive and conservative. Constructive is when two plates move away from each other, they correspond to mild earthquakes. When two plates move towards each other and collide, this is known as destructive plate boundaries. This is very destructive. Conservative corresponds to passing by of plates of crust. Earthquakes of this type have varying intensities.
3. Geological Faults
A geological fault is known as the displacement of plates of their original plane. The plane can be horizontal or vertical. These planes are not formed suddenly but slowly develop over a long period. The movement of rocks along these planes brings about tectonic earthquakes. These faults occur due to the impact of geological forces. The displacement of plates creates the fracturing of rocks, which releases a lot of energy. This type of earthquake can be disastrous.
4. Man Made
The interference of man with nature can also become a cause of the earthquake. The disturbance of crustal balance due to heavy clubbing of water in dams can cause earthquakes. Nuclear bombing can send specific type of shockwaves throughout the surface of the earth, which can disturb the natural alignment of tectonic plates. Mining can also cause disturbance due to the extensive removal of rocks from different areas.
5. Minor Causes
Some minor causes such as landslides, avalanches, the collapse of heavy rocks, etc. can also cause minor shockwaves. The gases beneath the surface of earth contract and expand, giving rise to movements in plates beneath the crust. The plutonic earthquake occurs because of adjustments in rock beds in the interior of earth’s crust. All these factors, correspond to minor earthquakes but sometimes these can also vary to moderate earthquakes.